Method of stabilizing composite media and media produced thereby

ABSTRACT

There is provided composite media and a method of producing them. The composite media contain a coalesced composite mixture of particles of an active ingredient and binder particles. The binder particles preferably also fuse the composite structure to front and back substrates. The composite media also have stabilizing particles that fuse with both the particles of an active ingredient and the substrates, thereby forming a composite medium according to the present invention.

[0001] This application is a continuation-in-part of co-pending U.S.patent application Ser. No. 08/903,395, filed Jul. 22, 1997, which is adivision of U.S. patent application Ser. No. 08/8 13,055, filed Mar. 7,1997 (issued as U.S. Pat. No. 5,792,513).

FIELD OF THE INVENTION

[0002] The present invention relates generally to activated media. Moreparticularly, the present invention relates to a method of stabilizingactivated media and media produced thereby.

BACKGROUND OF THE INVENTION

[0003] It is often desirable to impregnate, cover, or otherwise treat abase material with an active or activated material, such as an absorbentor adsorbent material. One example would be a non-woven medium coatedwith agents having fluid adsorption and/or odor adsorptioncharacteristics, as found in children's diapers, adult incontinenceproducts, feminine hygiene products, and other adsorbent articles ofclothing. Other examples include coated paper tissues and toweling, aswell as surgical bandages and sanitary napkins. Other materials may beused as adsorbent materials, such as cyclodextrins or zeolites for odorcontrol, or other adsorbents such as silicates, aluminas, or activatedcarbons.

[0004] The active, i.e., adsorbent, materials used to coat a basematerial may be fibrous or particulate materials. However, certainmaterials known in the art (e.g., fluff pulp fibers) have limitedadsorption capacity, and hence perform disappointingly during normalwear. In addition, products containing such materials are often heavyand/or bulky. Thus, it is preferable to use at least some portion ofparticles composed of super adsorbent polymers (SAP).

[0005] Yet, it is difficult to immobilize powdered or small granularparticles of SAP. Historically, microscopic active materials wereimmobilized on foams or on surfaces coated with a thin layer ofpressure-sensitive adhesive. U.S. Pat. No. 5,462,538 to Korpman is anexample of a method of immobilizing adsorbent material on a surfacecoated with a thin layer of pressure-sensitive adhesive. Using thismethod may produce large gaps between individual microscopic adsorbentelements. Also, the resulting adsorbent core has only a single layer ofadsorbent material. PCT Publication No. WO 94/01069 to Palumbo isanother example of a method of immobilizing particulate adsorbentmaterial. However, the adsorbent particles are not bonded to thesubstrates. Moreover, the adsorbent particles are not in significantcontact with the binder particles. Thus, neither method effectivelyrestrains powdered or small granular particles of an active ingredient.

[0006] As a more effective alternative, U.S. Pat. No. 5,792,513, whichis fully incorporated herein by reference, discloses a product formedfrom a composite mixture of adsorbent particles and binder particlesfused to a substrate. While this product provides excellent absorptioncharacteristics, the particles swell when exposed to fluid and thenseparate from the substrate and each other during normal use. This loosematerial is then free to slump or move.

[0007] In light of the foregoing, there remains a need for media, and amethod of producing such media, in which the particles of an activeingredient are substantially immobilized even after they have becomeswollen, while maintaining excellent composite integrity.

SUMMARY OF THE INVENTION

[0008] The present invention provides an improved composite medium, inwhich the particles of an active ingredient are substantiallyimmobilized. A further object is to provide absorbent or adsorbentarticles having stabilizing particles dispersed throughout a coalescedcomposite layer of particles of an active ingredient and binderparticles. By substantially immobilizing the particles of an activeingredient the present invention effectively prevents migration of theparticles of an active ingredient, thereby creating an adsorbent productwith enhanced integrity throughout the use cycle of the product.

[0009] Accordingly, the present invention provides composite media and amethod of producing them. The composite media contain a coalescedcomposite mixture of particles of an active ingredient and binderparticles. The binder particles preferably also fuse the compositestructure to front and back substrates. The composite media also havestabilizing particles that fuse with both the particles of the activeingredient and the substrates, thereby forming a composite mediumaccording to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a side plan-view of the composite media of the presentinvention; and

[0011]FIG. 2 is a schematic diagram illustrating an apparatus for thepractice of the method of this invention.

DETAILED DESCRIPTION OF THE INVENTION

[0012] Referring to the drawings and, in particular, FIG. 1, there isprovided a composite medium generally indicated as 1. Composite medium 1has a backing substrate 10 and a covering substrate 20.

[0013] Backing substrate 10 and covering substrate 20 may be formed ofvarious materials depending upon the application. By way of example,substrates 10, 20 may be a permeable material, such as a non-wovenfibrous material, e.g., spun-bonded polyester or polyolefin. Wovensubstrates may also be used. Furthermore, substrates 10, 20 mayoptionally be formed using cellulosic materials, such as paper, or acombination of cellulosic and thermoplastic fibers. Either substrate 10or 20 may also be an impermeable material, such as a plastic film (e.g.,Mylar(®)), a permeable backsheet or membrane or another suitablematerial.

[0014] The particular material selected for substrates 10, 20 can alsoeffect the kinetics of adsorption of composite medium 1. For example,substrates 10, 20 can modify the mean pore size and the overallporosity, provide supplemental adsorption, improve tensile strength,flexibility, and pleatability, and effect wicking and fluiddistribution.

[0015] Between substrates 10, 20, there is a layer, generally indicatedas 2. Layer 2 has particles of an active ingredient 30, binder particles40, and stabilizing particles 50. Particles of an active ingredient 30are coalesced or fused together by binder particles 40. An amount ofbinder particles 40 may also be fused to points on either substrates 10or 20, thereby also binding particles 30 to substrates 10 and 20.However, binding particles 40 will only be fused with one of substrates10 and 20, rather than both. Stabilizing particles 50 may also be bondedto particles of an active ingredient 30 and, in contrast to bindingparticles 40, are fused to both backing substrate 10 and coveringsubstrate 20, thereby forming a stabilizing bond or quilting effect.

[0016] The thickness of layer 2 will vary depending on a variety offactors, including the size of the particles 30, 40, and 50, thequantity of particles 30, 40, and 50, the degree of coalescence betweenparticles 30, 40, and 50, and whether other particles or fibers, such asfluff pulp, are used in layer 2. Preferably, the thickness of layer 2 isabout 0.2 mm to about 5 mm.

[0017] Particles of an active ingredient 30 can potentially be formed ofany material. For example, particles of an active ingredient 30 mayabsorb or adsorb fluids or gases. Furthermore, particles of an activeingredient 30 may be used to release fluids or gases held therein, forexample, to deliver fluids, such as medicaments. Materials such asiodinated resin, activated carbon, activated alumina, aluminum powders,nickel powders, alumina-silicates, ferromagnetic materials, ion-exchangeresins, manganese or iron oxides, zeolites, glass beads, ceramics,diatomaceous earth, and cellulosic materials can also be used asparticles of an active ingredient 30. In addition, particles of anactive ingredient 30 may also be polymeric materials, such as SAP. Thecross sectional size of particles of an active ingredient 30 ispreferably within a range of about 5 microns to about 5000 microns.

[0018] Materials forming binder particles 40 may potentially include anymaterial known in the art. In particular, thermoplastic and thermosetmaterials are useful for the practice of the present invention. Forexample, binder particles 40 may be polyethers, polyolefins, polyvinyls,polyvinyl esters, polyvinyl ethers, ethylene-vinyl acetate copolymers,or a mixture thereof. Also, suitable binder particles may be producedfrom particulate thermoset resins known in the art, such asphenol-formaldehyde or melamine resins, with or without additionalcrosslinking agents. Preferably, binder particles 40 are present in suchan amount and at such a size that they do not substantively interferewith the functioning of particles 30. Binder particles 40 are preferablyabout 5 microns to about 50 microns in size.

[0019] The critical feature of this invention resides in stabilizingparticles 50 that are used to form through-web stabilizing bonds withinlayer 2. First, stabilizing particles 50 perform a similar function asbinder particles 40, specifically coalescing or fusing togetherparticles of an active ingredient 30. However, they are extremelylimited in their capacity to stabilize the active ingredient particlesbecause they are large and provide limited surface area to interfacewith the active ingredient and they are generally present in smallamounts, again limiting their ability to stabilze other particles.Stabilizing particles 50 are also adhered or fused to both substrates10, 20 because they are selected to have a particle size roughly equalto or greater than the thickness of layer 2. Materials formingstabilizing particles 50 are potentially any suitable material, such asthe materials listed in reference to binding particles 40, e.g., athermoplastic or a thermoset material. Stabilizing particles 50 arepreferably present in such an amount and at such a size that they do notsubstantively interfere with the functioning of particles of an activeingredient 30 and binder particles 40. It is preferred that stabilizingparticles 50 be both larger in size and fewer in number compared tobinder particles 40. Preferably, stabilizing particles 50 are equal toor larger than the thickness of layer 2, so as to allow stabilizingparticles 50 to span the entire thickness of layer 2 and directly adhereto substrates 10, 20. However, stabilizing particles may be smaller thanthe thickness of layer 2, for instance, if a ribbed effect for compositemedium 1 is desired. In addition, stabilizing particles may beintimately grouped together, thereby binding to both substrates 10, 20in the aggregate.

[0020]FIG. 2 illustrates an exemplary apparatus for the practice of thisinvention. A supply roll 100 provides a substrate 120 to be treated,such as a nonwoven tissue or toweling paper. Downstream from supply roll100 is a knurled roller 130 positioned to receive a mixture of particlesof an active ingredient 30, binder particles 40, and stabilizingparticles 50, the mixture generally being indicated as 140 and dispensedfrom a hopper 160. Mixture 140 is applied to the upper surface ofsubstrate 120 as a continuous coating or, alternatively, as a coating ofa specific design such as, for example, stripes. A brush 180 may beemployed to aid in removing mixture 140 from knurled roller 130.Thereafter, substrate 120 is passed through a nip 200 between a heatedidler roller 220 and a drive roller 240. Alternatively, before beingpassed through nip 200, substrate 120 may also be preheated, forexample, by a convection or infrared oven. A pneumatic cylinder isconnected via a rod 280 to the axle of idler roller 220 to maintain adesired pressure on substrate 120 within nip 200. In passing over thesurface of heated roller 220, mixture 140 is heated to a temperatureequal to or greater than the softening temperature of binder particles40 and stabilizing particles 50, but lower than the softeningtemperature of particles of an active ingredient 30. Within nip 200,binder particles 40 and stabilizing particles 50 fuse under pressurewith particles of an active ingredient 30, while stabilizing particles50 also fuse with substrate 120. An amount of binder particles 40 mayfuse with substrate 120. Furthermore, in a preferred alternative to theabove described apparatus, a second supply roll 300 of a substrate 320,which may be of the same or a different material from that of substrate120, is also passed between nip 200 on the top of mixture 140.Stabilizing particles 50 fuse with substrate 320 and an amount of binderparticles 40 may also fuse with substrate 320. However, whilestabilizing particles 50 fuse with both substrate 120 and 320, binderparticles 40 will only fuse with either substrate 120 or 320. Uponleaving the nip 200, binder particles 40 and stabilizing particles 50cool and harden. The composite medium 240 passes onto a takeup roll 360.

[0021] Coalescing particles of an active ingredient 30 with interposedbinder particles 40 and stabilizing particles 50 results in morecomplete coverage of the backing substrate 10 and places particles of anactive ingredient 30 in closer proximity to each other. In addition, itis possible to vary the depth and porosity of layer 2 and to havemultiple layers of active ingredient fully stabilized by binderparticles 40. When composite layer 1 contains SAP and is wetted, the SAPparticles swell and generally break their bonds with binder particles 40and any bonds that might exist with stabilizing particles 50. However,the bonds between substrates 10 and 20 and stabilizing particles 50 areretained and prevent the wholesale disassembly of composite layer 1.These stable bonds do not prevent local swelling of the composite layer1, but do provide localized stabilization of composite layer 1 at eachpoint where stabilizing particle 50 spans composite layer 1. These bondsprovide a random quilting effect that prevents the movement of theswollen SAP mass.

[0022] Although composite medium 1, and the method of producing such amedium, has been described with respect to one or more particularembodiments, it will be understood that other embodiments of the presentinvention may be employed without departing from the spirit and scope ofthe present invention. Hence, the present invention is deemed limitedonly by the appended claims and the reasonable interpretation thereof.

What is claimed is:
 1. A composite medium comprising: a backing sheet; acovering sheet; and a layer disposed between said backing sheet and saidcovering sheet, said layer having particles of an active ingredient,binder particles and stabilizing particles, wherein said activeparticles are coalesced by said binder particles, and wherein each ofsaid stabilizing particles forms a bond with both said backing sheet andsaid covering sheet.
 2. The composite medium of claim 1, wherein saidbacking sheet is an impermeable material.
 3. The composite medium ofclaim 1, wherein said backing sheet is a permeable material.
 4. Thecomposite medium of claim 1, wherein said covering sheet is a permeablematerial.
 5. The composite medium of claim 1, wherein said compositelayer has an average thickness of about 0.2 mm to 5 mm.
 6. The compositemedium of claim 1, wherein said particles of an active ingredient areformed from at least one component selected from the group consistingone of: adsorbent particles, absorbent particles, particles that releaseliquid or gases held therein, and mixtures thereof.
 7. The compositemedium of claim 1, wherein said particles of an active ingredient areformed from at least one component selected from the group consistingone of: iodinated resin, activated carbon, activated alumina,alumina-silicates, ion-exchange resins, manganese oxides, iron oxides,zeolites, hydrophilic polymeric materials, and mixtures thereof.
 8. Thecomposite medium of claim 1, wherein said particles of an activeingredient have an average particle size of between about 5 microns to5000 microns.
 9. The composite medium of claim 1, wherein said binderparticles are formed from at least one component selected from the groupconsisting one of thermoplastic materials, thermoset materials, andcombinations thereof.
 10. The composite medium of claim 1, wherein saidbinder particles are formed from at least one component selected fromthe group consisting of: polypropylene, linear low-density polyethylene,low density polyethylene, ethylene-vinyl acetate copolymer, polyolefin,phenol-formaldehyde resin, melamine resin, and mixtures thereof.
 11. Thecomposite medium of claim 1, wherein said binder particles have anaverage particle size of between about 5 microns to 50 microns.
 12. Thecomposite medium of claim 1, wherein said stabilizing particles areformed from at least one component selected from the group consisting ofthermoplastic materials, thermoset materials, and combinations thereof.13. The composite medium of claim 1, wherein said stabilizing particlesare formed from at least one component selected from the groupconsisting of polypropylene, linear low-density polyethylene, lowdensity polyethylene, ethylene-vinyl acetate copolymer, polyolefin,phenol-formaldehyde resin, melamine resin, and mixtures thereof.